The present invention is related to an electric drive device for an electric power steering system of automotive vehicles.

Electric power steering (EPS) systems of automotive vehicles, which assist in moving the steering wheel of automotive vehicles, are known in the state of the art. The assistance in moving the steering wheel consists of the EPS system delivering mechanical torque to the steering column of the automotive vehicle. In order to be able to generate the delivery torque, the EPS system comprises an electric drive device, said device comprising an electric motor generating mechanical torque. The electric motor is usually a three-phase alternating current (AC) motor, but the electric drive device is powered with direct current DC from the vehicle, so it is necessary to convert said direct current into three-phase alternating current, and it is furthermore necessary to control the drive of the electric motor, so the electric drive device needs an electronic control unit close to the electric motor.

EP2549627 A1 discloses an electric drive device for an EPS system, comprising an electric motor with a motor case, a stator arranged inside the motor case providing a plurality of phases, a rotor arranged rotatably in relation to the stator, and a motor shaft that rotates together with the rotor with a drive end of the output torque of the motor projecting from the motor case. The device also comprises an electronic control unit, after the motor, controlling the drive of the motor, comprising a power board supplying current to the motor, and a control board electrically connected to the power board controlling the drive of the motor through the power board, and a heat sink absorbing and dissipating the heat generated by the power board. The heat sink, the power board and the control board are arranged after the motor in the mentioned order.

JP2002345211 A discloses an electric drive device for an electric power steering system according to the preamble of claim 1.

The object of the invention is to provide an electric drive device for an EPS system as defined in the claims.

The electric drive device of the invention comprises an electric motor with a motor case, a stator arranged inside the motor case providing a plurality of phases, a rotor arranged rotatably in relation to the stator, and a motor shaft that rotates together with the rotor with a drive end of the output torque of the motor projecting from the motor case. The device also comprises an electronic control unit controlling the drive of the motor, comprising a power board supplying current to the motor, and a control board electrically connected to the power board controlling the drive of the motor through the power board, and a heat sink absorbing and dissipating the heat generated by the power board. The heat sink, the power board and the control board are arranged after the motor in the mentioned order. In said electric drive device, the power board covers the cross section of the motor case.

Since the power board is arranged so as to cover the cross section of the motor case, it allows arranging the distinct elements of said power board such that they are better distributed in a single part and facing the heat sink. Therefore on one hand, the number of parts of the electric drive device is reduced because the power board covers a larger surface in a single part. On the other hand, heat dissipation, and therefore thermal efficiency, of the electric drive device improves, because the motor, which generates heat, discharges said heat perimetrally towards the motor case, and the heat arriving to the heat sink is mainly from the power board located on said heat sink. A more compact design of the electric drive device is further obtained because by covering the cross section of the motor case as the elements of the power board are arranged in said cross section a smaller power board is obtained.

These and other advantages and features of the invention will become evident in view of the drawings and the detailed description of the invention.

• Figure 1 shows a perspective view of an embodiment of an electric drive device of the invention.
• Figure 2 shows an elevational view of the device of Figure 1.
• Figure 3 shows a longitudinal section view according to line III-III of the device of Figure 2.
• Figure 4 shows an exploded view of the main parts of the device of Figure 1.
• Figure 5 shows a perspective view of the outer side of the second part of an embodiment of the heat sink of the device of Figure 1.
• Figure 6 shows a longitudinal section view of the device of Figure 1 with a second embodiment of the heat sink.
• Figure 7 shows an exploded view of the main parts of the device of Figure 6.
• Figure 8 shows a detailed view of the heat sink of the device of Figure 6.
• Figure 9 shows a front perspective view of an embodiment of the connector of the device of Figure 1.
• Figure 10 shows a rear perspective view of the embodiment of the connector of Figure 9.
• Figure 11 shows a front perspective view of a second embodiment of the connector of the device of Figure 1 without ground connections.
• Figure 12 shows a rear perspective view of the embodiment of the connector of Figure 11.
• Figure 13 shows a block diagram showing the communications of the main parts of the power board and the control board of the device of Figure 1.

Figure 1 shows a perspective view of an embodiment of an electric drive device of the invention, Figure 2 shows an elevational view of the device of Figure 1, Figure 3 shows a longitudinal section view according to line III-III of the device of Figure 2, Figure 4 shows an exploded view of the main parts of the device of Figure 1, and Figure 5 shows a perspective view of the outer side of the second part of an embodiment of the heat sink of the device of Figure 1.

The electric drive device 100 of the invention is applied to an electric power steering (EPS) system of an automotive vehicle. Said device 100 comprises an electric motor 1 arranged inside a motor case 2 made of aluminum. The motor 1 is the power supply source of the EPS system, said motor 1 in this embodiment being a three-phase brushless alternating current (AC) motor. Said motor 1 basically comprises a stator 3 arranged inside the motor case 2, a rotor 5 arranged rotatably in relation to the stator 3 therein, and a motor shaft 6 that rotates together with the rotor 5 in an integral manner, said motor shaft 6 comprising a drive end 7 of the output torque of the motor 1 projecting from the motor case 2.

The rotor 5 is a permanent magnet-type rotor with a plurality of poles, and the stator 3 includes a plurality of projecting poles arranged facing the permanent magnet of the rotor 5 around same. The stator 3 comprises a plurality of windings arranged around the poles of the stator 3, and three phases 4 (U, V, W) with terminals projecting from the motor case 2 are connected to these windings.

In this embodiment of the device 100, the motor case 2 has a substantially cylindrical shape. It comprises a side wall 102 and an end 105 with a lid 106 formed in the actual motor case 2, where the drive end 7 of the motor shaft 6 projects. The device 100 is used by an EPS system to provide assistance in moving the steering wheel of an automotive vehicle, said assistance consisting of the EPS system delivering mechanical torque from the steering column of the automotive vehicle. In order to generate the delivery torque, the EPS system comprising the electric drive device 100 has an electric motor 1. This motor 1 generates the mechanical torque and delivers it through the drive end 7 of the motor shaft 6. This drive end 7 is coupled to a reduction gear of the EPS system (not shown in the drawings), which in turn is connected to the steering column of the vehicle. Therefore, when the vehicle driver operates the steering wheel a mechanical torque is generated in the steering column that is detected by a torque sensor (not shown in the drawings). The detected torque is sent as a signal to the device 100, which generates a mechanical torque by means of the electric motor 1, said torque being transmitted to the reduction gear of the EPS system, and this EPS system transmits it to the steering column of the vehicle, assisting the driver in moving the steering wheel.

In order to perform those operations in a controlled manner, the device 100 also comprises an electronic control unit 10 controlling the drive of the motor 1 with the electric current supply. The electronic control unit 10 comprises a power board 20 with semiconductor switching elements 23, 25, 27 supplying current to drive the motor 1, and a control board 70 electrically connected to the power board 20 controlling the drive of the motor 1 through the power board 20. The device 100 also comprises a heat sink 40, 40' made of highly thermally conductive aluminum, absorbing and dissipating the heat generated mainly by the power board 20 through the semiconductor switching elements 23, 25, 27. Furthermore, the electric drive device 100 comprises a cover 50 which covers the electronic control unit 10 and closes it at one end 53 against an end 101 of the motor case 2. The assembly of the device 100 is therefore a compact unit formed by the motor case 2 and the cover 50, the motor 1, the heat sink 40, 40', the power board 20 and the control board 70 being arranged in the mentioned order with respect to the drive end 7 of the motor shaft 6. The power board 20, which is located after the heat sink 40, 40', covers the cross section of the motor case 2. In document EP2549627 A1, the power board containing the semiconductor switching elements only partially covers the cross section of the motor, whereas the device 100 of the invention covers all or most of said cross section. This allows arranging the distinct elements of said power board such that they are better distributed in a single part and facing the heat sink.

In this embodiment, the heat sink 40, 40' is a substantially cylindrical part acting as a cover of the motor case 2 at the end 101, and therefore is another element of said case 2. In this embodiment of the device 100, the heat sink 40; 40' comprises a substantially planar outer side 47, 49 distributed in a substantially uniform manner, facing and adjacent to the power board 20. The heat sink 40, 40' is arranged at the end 101 of said motor case 2, on the side opposite the lid 106 of the case 2, and thus closes the cylindrical shape of the motor case 2. The heat sink 40; 40' acting as closure lid of the motor case 2 comprises an inner side 46; 64 that is located inside the motor case 2. Said heat sink 40; 40' does not project or slightly projects from the motor case 2.

A position end 8 of the motor shaft 6, which is opposite the drive end 7 of said motor shaft 6, and therefore below the inner side 46; 64 of the heat sink 40; 40', is located at the end 101 of the motor case 2 and inside the motor case 2.

Figure 6 shows a longitudinal section view of the device 100 of Figure 1 with a second embodiment of the heat sink 40, Figure 7 shows an exploded view of the main parts of the device 100 of Figure 6, and Figure 8 shows a detailed view of the heat sink 40 of the device of Figure 6. In this embodiment, the heat sink 40 having a substantially cylindrical shape comprises two parts. A first part 48 is supported in the motor case 2, the inner side 46 of which comprises support means 42. These support means 42 comprise a housing 43 arranged substantially in the center of the first part 48, the housing 43 being open towards the outside of the motor case 2, and wherein a bearing 110 supporting the position end 8 of the motor shaft 6 is fitted. A second part 45 of the heat sink 40 is arranged on the first part 48, covering the housing 43, and has a through hole 41 in the center having a diameter that is smaller than the opening of the housing 43. The heat sink 40 thus comprises the outer side 47, which is the free outer surface of the first part 48. The first part 48 is made of a highly thermally conductive material, such as aluminum for example, and the second part 45 is a metal part made of pressed steel that has been subjected to anti-corrosion treatment, such as cataphoresis for example.

The embodiment of the heat sink 40' of Figures 3, 4 and 5 shows how said heat sink 40' also has a substantially cylindrical shape and comprises two parts. A first part 68 is supported in the motor case 2, the inner side 64 of which comprises support means 62. These support means 62 comprise a housing 63 arranged substantially in the center of the first part 68, the housing 63 being open towards the outside of the motor case 2, and wherein a bearing 110 supporting the position end 8 of the motor shaft 6 is fitted. A second part 65 of the heat sink 40 is arranged on the first part 68, covering the entire surface of the first part 68, and covering the housing 63, and has a through hole 61 in the center having a diameter that is smaller than the opening of the housing 63. The heat sink 40' thus comprises the outer side 49, which is the free outer surface of the second part 65. Both the first part 68 and the second part 65 are made of a highly thermally conductive material, such as aluminum for example.

In both embodiments of the heat sink 40; 40', the drive end 7 of the motor shaft 6 is housed in another bearing arranged in support means of the lid 106 of the motor case 2. The bearing 110 is housed in the housing 43; 63 from the outside of the motor case 2 and once the first part 48; 68 is assembled in said motor case 2. The heat sink 40; 40' comprises a second part 45; 65 which covers the hole of the housing 43; 63, demarcating a hole 41; 61, having a smaller diameter than the hole of the housing 43; 63, preventing accessibility to the housing 43; 63, and thus completing the dissipation surface of the power board 20. The bearing 110 is thus assembled in the housing 43; 63 of the heat sink 40; 40' from the outside, and next the second part 45; 65 is assembled in the heat sink 40; 40'. Therefore, when the motor shaft 6 is assembled, the position end 8 is located inside the housing 43; 63 of the heat sink 40; 40' and is substantially flush with the outer side 47; 49 of the heat sink 40; 40'. The position end 8 of the motor shaft 6 comprises a magnet 9, and the power board 20 comprises a magnetic sensor 30 on a lower side 21 facing the heat sink 40; 40' and substantially in the center, the magnetic sensor 30 facing the magnet 9 through the through hole 41; 61.

Once the heat sink 40; 40' is assembled in the motor case 2, next the power board 20 and the control board 70 are assembled, being arranged in the mentioned order in a substantially parallel manner, thereby obtaining a more compact structure of the device 100, taking up less space in the length thereof.

Figure 9 shows a front perspective view of an embodiment of the connector of the device of Figure 1, and Figure 10 shows a rear perspective view of the embodiment of the connector of Figure 9. The electric drive device 100 also comprises a connector 80 which allows connecting the electronic control unit 10 with the outside by wiring. To operate, the device 100 needs on one hand power, which can be supplied by the battery of the vehicle, and on the other hand information about the mechanical torque applied to the steering column of the vehicle to thus define the torque that must be generated and delivered by the device 100, and it also needs to be communicated with the vehicle in order to know the status of different functions thereof, such as for example the start of the vehicle, when it is moving or stopped, the speed of said vehicle, etc. To that end, said connector 80 comprises a power supply housing 81 receiving power from the outside, an electric torque signal housing 82 receiving the torque signal from the outside, and a communications housing 83 which allows receiving and sending communication signals. The connector 80 also comprises terminals 84 which allow directly connecting said connector 80 with the power board 20 through the power supply housing 81, and therefore supplying power from the battery of the vehicle. The connector 80 also comprises terminals 85 which allow connecting directly with the control board 70 through the electric torque signal housing 82, and therefore being able to send the torque signal to the control board 70, and terminals 86 which allow connecting directly with the control board 70 through the communications housing 83, thereby allowing communication from the outside to the control board 70.

The connector 80 also comprises ground connections 99, which in the embodiment shown in Figures 9 and 10 are two in number, attached to the negative connection of the battery of the vehicle through the terminals 84 of the power supply housing 81, and said ground connection is taken to the power board 20 and to the control board 70. The electric drive device 100 of the invention may not comprise said ground connections 99, as shown in a second embodiment of the connector 80 in Figures 11 and 12, but the operation of the device is more efficient with such connections because they improve radio emissions and the immunity of the device 100.

The connector 80 is attached to the device 100 laterally from the outside. The connector 80 comprises two areas, a first area 87 which is physically attached to the device 100, said first area 87 comprising the terminals 84, 85, and 86. It also comprises a second area 88 which is attached to the first area 87 and is arranged outside the device 100 when said device 100 is completely assembled. This second area 88 comprises the power supply housing 81, the electric torque signal housing 82, and the communications housing 83. In this embodiment, the first area 87 comprises two protrusions 89 projecting from the first area 87 in a plane perpendicular to the geometric axis of the motor shaft 6. The connector 80 is thus prepared for being assembled in a portion of the device 100 which comprises housings that allow housing the protrusions 89. Since the connector 80 comprises two areas 87 and 88, once the connector 80 is assembled in the device 100, it allows the first area 87 to be concealed in the device 100 and the second area 88 to be accessible from the outside to enable being connected with the housings 81, 82 and 83. Therefore, and according to the connection requirements of each customer, the outer design can be modified without modifying the design of the power board 20 and control board 70.

In the embodiments shown in Figures 4, 5, 7 and 8, the heat sink 40; 40' comprises two lobe-shaped housings 90 arranged on an edge 91 of the periphery of said heat sink 40; 40'. Once the device 100 is assembled with the motor 1, the heat sink 40; 40', the power board 20 and control board 70, the housings 90 of the heat sink 40; 40' are in view and allow housing the protrusions 89 of the first area 87, which in this embodiment have the same identical lobe shape as the housings 90 of the heat sink 40; 40'. The protrusions 89 are assembled in the housings 90 from top to bottom, and extraction of the protrusions 89 in the radial direction, and therefore extraction of the connector 80 when the device 100 is assembled, is thereby prevented. With this design of the device 100, the connector 80 can be inserted and fixed without requiring fixing means, such as screws for example.

The outer side 47; 49 of the heat sink 40; 40' comprises a vertical edge 92 running along the periphery of said outer side 47; 49 in a segment that is not attached to the connector 80. The connector 80 comprises a vertical edge 93 on the upper surface of the first area 87 running along the area of intersection of said first area 87 with the second area 88. Said edges 92 and 93 are defined such that the ends of the vertical edge 92 of the heat sink 40; 40' and the ends of the vertical edge 93 of the connector 80 coincide when the connector 80 is assembled in the heat sink 40; 40', thereby forming a single edge.

In these embodiments, the heat sink 40; 40' comprises three seats 94 with holes 95 substantially parallel to the geometric axis of the motor shaft 6. Said seats 94 are arranged along the periphery of the outer side 47; 49 and are substantially spaced from one another. The motor case 2 at the end 101 of the side wall 102 comprises three seats 103 with holes 104 which are also substantially parallel to the geometric axis of the motor shaft 6. These seats 103 with their holes 104 coincide with the seats 94 and the holes 95 of the outer side 47; 49 of the heat sink 40; 40' when said heat sink 40; 40' is assembled in the motor case 2. On the other hand, the cover 50 of the device 100 comprises three seats 51 with holes 52 which are also substantially parallel to the geometric axis of the motor shaft 6, these seats 51 projecting radially from the end 53 of the cover 50. When the electric motor 1, the heat sink 40; 40', the power board 20 and the control board 70 are assembled in the device 100, it is necessary to lastly assemble the cover 50, and thus protect the device 100 against external conditions, such as moisture, dirt and also electromagnetic radiation. To that end, the cover 50 is arranged on the power board 20 and the control board 70, and its end 53 is assembled against the motor case 2, attaching the seats 51 of the cover 50 with the seats 94 of the heat sink 40; 40' with attachment means, such as screws for example, the cover 50 overlapping in that assembly with the single edge formed by the vertical edge 92 of the heat sink 40; 40' and the vertical edge 93 of the connector 80. Movement of the connector 80 in the axial direction is thereby also prevented when closing the cover 50 on the motor case 2, which prevents the entrance and exit of electromagnetic radiation as well as the entrance and exit of external elements such as dirt, and it prevents the transmission of vibrations caused by outer cables.

Figure 13 shows a block diagram showing the communications of the main parts of the power board and control board of the device of Figure 1. The control board 70 and power board 20, as well as the electric motor 1, are depicted in this block diagram. The torque signal inputs through the torque signal housing 82 of the connector 80 and the communication inputs through the communications housing 83 of the connector 80 are arranged in the control board 20. The torque signal housing 82 comprises three torque signal pins which allow having said torque signal in a doubly redundant manner and sending it to the microprocessor 73. It also comprises a pin as INDEX which allows sending a signal to the microprocessor 73, indicating the zero-crossing of the steering wheel. It also comprises four torque signal supply pins, two of which feed the torque sensor and the other two of which feed the INDEX, receiving a signal from the power source 75 of the control board 70 and from the microprocessor 73.

The communications housing 83 comprises a vehicle start signal input as IGNITION, said signal passing to the communications supervision device 74 SBC, and an input for the CAN communications bus, which is reciprocal between the communications housing 83 and the device 74.

The SBC device receives direct power from the battery BAT of the vehicle after being filtered by the choke coil 32 of the power board 20. There is reciprocal communication from the SBC device with the microprocessor 73, the SBC device performing monitoring functions, and it also communicates with the microprocessor 73 through a re-initializer R. The SBC device can also send secure signals to a control device 77 of the solid-state phase relays 26 and of the power supply relays 28.

In addition to the mentioned signals, the microprocessor 73 receives power from the power source 75 at 3V3, receiving a 5V analog signal as a reference, and a 5V monitoring signal for making sure that the torque sensor is correctly fed. The microprocessor 73 sends signals to the control device 77 and receives signals from the temperature sensor ST, from the shunts 29, from the magnetic angle sensor 30 that is fed from the battery BAT through a linear voltage regulator LDO, and from a timer T.

The power board 20 receives the power input from the battery BAT of the vehicle through the external power supply housing 81 of the connector 80. The choke coil 32 which allows eliminating noises and interferences is powered from said housing 81, said power supply being transmitted from the choke coil 32 to the control board 70 through a connector between boards (not depicted in the drawings), and to the input of the power supply relays 28. These relays 28 comprising the semiconductor switching elements 27 receive excitation from a drive circuit 38, which in turn receives communication from the control device 77, and they allow passage of the flow of direct current DC towards the power filter 33. Said power filter 33 comprises a coil 34 and two capacitors 35 and allows filtering interferences.

This power filter 33 feeds the inverter 24 in which the temperature sensor ST is arranged and mainly the inverter circuit 24. This inverter circuit 24 comprising the semiconductor switching elements 23 allows converting direct current DC into three-phase alternating current AC powering the motor 1. The shunts 29 which allow measuring the flow of electric current towards the motor 1 are also arranged in this inverter 24, sending the signal indicating the level of current circulating through the shunts 20 to the microprocessor 73, such that the microprocessor makes decisions according to said level. The inverter 24 receives excitation from the drive circuit 36 which in turn receives signals from and sends them to the microprocessor 73.

Finally, and after the electric current passes through the inverter 24 and is converted to three-phase alternating current AC, the phase relays 26 comprising the semiconductor switching elements 25 are powered, and they receive excitation from the drive circuit 37, which in turn receives communication from the control device 77. The three-phase alternating current AC powers the three phases 4 (U, V, W) of the electric motor 1. The electric motor 1 comprising the shaft 6 has a magnet 9 generating a magnetic field in the position end 8, and the power board 20 comprises the magnetic sensor 30 which senses said magnetic field and thereby determines the position of the motor shaft 6. This intercommunication is depicted in the block diagram of Figure 13 by means of an arrow heading away from the motor 1 towards the angle sensor 30.